Copper-lead alloys

ABSTRACT

A method of making a copper-lead alloy having a fine and even dispersion of the phases and the alloy and its uses, wherein the method comprises adding an effective amount of a homogeneity promoter to a mixture of molten lead and copper. The promoter comprises elemental carbon and an alkali and/or alkaline earth metal compound capable of reacting to form a gas. The mechanism provided by the promoter is one of innoculation of a fine dispersion of the lead particles in a copper matrix. Examples of the metal compound are sodium carbonate and calcium carbonate. Uses for the alloy include bearings, lubricants and as an additive to petroleum and vegetable based lubricating compounds.

United States Patent [191 Lundin et al.

[ 1 COPPER-LEAD ALLOYS [75] Inventors: Charles E. Lundin, Evergreen; Robert Turkisher, Manitou Springs, both of C010.

[73] Assignee: Colorado Springs National Bank,

Colorado Springs, Colo.

[ Notice: The portion of the term of this patent subsequent to Jan. 19, 1988, has been disclaimed.

[22] Filed: July 10, 1970 [21] Appl. No.: 53,953

Related U.S. Application Data [63] Continuation-impart of Ser. No. 706,640, Feb. 19,

1968, Pat. No. 3,556,779.

[52] U.S. Cl. ..75/135, 75/163, 75/166 E [51] Int. Cl. ..C22c 9/48 [58] Field of Search ..75/135, 163, 166 E [56] References Cited UNITED STATES PATENTS 825,100 7/1906 Yunck ..75/76 1*Marcb 6, 1973 Primary ExaminerCharles N. Lovell Assistant Examiner-E. L. Weise AttorneyKenyon & Kenyon Reilly Carr & Chapin 5 7 ABSTRACT A method of making a copper-lead alloy having a fine and even dispersion of the phases and the alloy and its uses, wherein the method comprises adding an effective amount of a homogeneity promoter to a mixture of molten lead and copper. The promoter comprises elemental carbon'and an alkali and/or alkaline earth metalcompound capable of reacting to form a gas. The mechanism provided by the promoter is one of innoculation of a fine dispersion of the lead particles in a copper matrix. Examples of the metal compound are sodium carbonate and calcium carbonate. Uses for the alloy include bearings, lubricants and as an additive to petroleum and vegetable based lubricating compounds.

15 Claims, 2 Drawing Figures COPPER-LEAD ALLOYS CROSS-REFERENCES This application is a continuation-in-part of our copending application Ser. No. 706,640 filed Feb. 19, 1968 now U.S. Pat. 3,556,779 dated Jan. 19, 1971.

This invention relates to alloys and in particular to copper-lead alloys and methods of making them and different uses thereof. The term homogeneous is used herein to refer to an improved alloy having a fine and even dispersion of the phases.

Attempts to produce homogeneously dispersed copper-lead alloys have been made in order to provide such alloys which have high thermal conductivity, low electrical resistivity and a low coefficient of friction. These properties are highly desirable for metals used to make bearings or as a bearing material and as a dry lubricant or as an additive to liquid or viscous lubricants made of petroleum or vegetable bases. However, many problems have not been solved by the prior art in attempting to make homogeneously dispersed copper- A lead alloys. The basic problem with these alloys is the prevention of massive separation and segregation of the copper and lead. This tendency to separate and segregate increases as the lead content rises in the copper-lead alloy. Another problem associated with the use of prior alloys is that even if there is initial homogeneity, under high stress and temperature conditions, the lead has a tendency to separate and segregate from the copper. A further problem associated with copper-lead alloys in the prior art is that the lead tends to segregate from the copper when it is being remelted and recast into other shapes and forms.

It is therefore an object of the present invention to provide a copper-lead alloy with improved homogeneity of the phases.

Another object of the present invention is to provide a copper-lead alloy in which separation and segregation of lead from copper is reduced on remelting.

Yet another object of the present invention is to provide a homogeneous copper-lead alloy which is useful for production of bearings and a bearing material, and for utilization as a dry lubricant or as an additive to petroleum and vegetable based lubricants.

Yet another object of the present invention is to provide a process for making the improved copper-lead alloy of the present invention.

These and other objects will be apparent from a reading of the specification and claims of this application.

Briefly, in accordance with the present invention, the foregoing and other objects are accomplished by adding effective amounts of a homogeneity promoter to the molten metal. The promoter consists essentially of elemental carbon and an alkali or alkaline earth metal compound which reacts under the molten conditions present during the alloying and casting of the copper and lead to form a gas. The mechanism provided by the promoter is one of innoculation of a fine dispersion of the lead particles in a copper matrix. Examples of such compounds are sodium carbonate, and calcium carbonate.

Copper-lead alloys are produced according to the present invention in varying proportions of copper and lead. The proportions may be varied as desired and as the specific application dictates. It has been found that alloys of substantial utility are those which contain 5 to 55 percent lead and to 45 percent copper. The problem of separation and segregation of the lead and copper is greatest with a high lead content. The promoter of this invention therefore provides its greatest utility at lead contents of from 20 to 45 percent. If the lubricating qualities of the alloy are to be increased, the proportion of lead should be in the higher range. If it is desirable to increase the strength of the material, a lesser proportion of lead should be utilized. Additional elements may be added for their wellknown enhancement of particular properties such as zinc, tin, nickel, etc., in amounts up to about 10 percent by weight of the alloy.

As to the homogeneity promoter of this invention, it has been found that the elemental carbon component is preferably finely powdered graphite. Although coarser carbon may be used, the larger particles tend to decrease the efficiency of the process, presumably due to reduced surface area to volume ratio. Other forms of carbon include bone-black, carbon-black, charcoal and the like.

The alkali metal compound may be lithium, potassium or sodium (or other metals of Group la of the Periodic Table), preferably combined as a carbonate. The alkaline earth compound may be calcium, strontium or barium (or other metal of Group 2a of the Periodic Table) preferably combined as a carbonate. Combinations of alkali and alkaline earth compounds may be used, for example,-a mixture of sodium and calcium carbonate. The amount of homogeneity promoter used must be at least that amount which ensures formation of a uniformly dispersed mixture of lead and copper which does not segregate on solidification. A preferred effective range of the proportions has been found to be about 1-5 grams of carbon or graphite powder and about 3-15 grams of metal compound for each pound of alloy. Below this proportion, improvements in homogeneity are obtained, but the effect is less pronounced when a very minor amount of promoter is used. Higher amounts of the homogeneity promoter may be used,-for example, up to 10 grams of graphite and 30 grams of the metal compound for each pound of alloy. Although these and even greater amounts provide an improved alloy in accordance with the present invention, the use of greater amounts from an economic standpoint is less attractive. The maximum proportion of the promoter is determined by characteristic requirements of the alloy, and economic considerations. 7

Although the exact mechanism is not completely un derstood, and patentability is not dependent thereupon, it is believed that the promoter is partially decomposed to form gases which provide a stirring and nucleation effect and that the undecomposed portion of the promoter also provides nucleation sites. The carbonate melts well below the reaction temperature range and decomposes at the higher temperatures into carbon monoxide gas and the metal oxide. The oxide in turn is reduced by the carbon to form additional carbon monoxide and metal. The metal may also be above its boiling point and released to gaseous form. The combined action of the gases cause the vigorous stirring action. Agitation continues through the cooling step and it is in this stage when the agitation is believed to be most effective. The agitation prevents gross separation of the lead and the copper phases and further provides many more nucleation sites for the solid, copper-rich dendrites to form from the liquid. The additional nucleation sites cause the final solidified structure to be fine-grained and further allows more efficient and homogeneous entrapment and entrainment of the lead phase in the copper matrix. Also, innoculation occurs by unreacted (or partially reacted) carbonate and graphite during stirring of the melt. The innoculation by these particles which are not fully decomposed to gases provides sites for the nucleation and growth of fine lead particles. The combined action promotes a random, fine-grained dispersion of lead in copper which is mandatory for the optimum characteristics and requirements of a bearing alloy. An additional benefit of the emission of carbon monoxide, or gaseous metal, is to produce a reducing atmosphere over the alloy during the liquification and solidification which almost completely prevents oxidation of the alloy from the air. Thus, it is not necessary to employ artificial protective atmospheres to reduce severe metal loss due to oxidation. However, if desired, inert atmospheres may be used in addition to blanket the system.

The process of this invention produces a novel copper-lead alloy which has a finer and more uniform dispersion of the lead in the copper. The composition of the alloy is from 5 to 55 percent lead, preferably 20 to 45 percent lead, 95 to 45 percent copper, preferably 80 to 55 percent copper, with up to percent of other metals, preferably zinc and/or tin, with only minor amounts of other metals, and trace amounts of the homogeneity promoter. The average particle size of the lead in the copper matrix is between 0.002 mm to 0.020 mm, diameter. Larger particles of lead occur but only a very minor amount of segregation occurs, which is not detrimental. An average particle size of 0.002 to 0.010 mm for copper-lead alloys'having 20 to 45 percent lead produces an excellent alloy in accordance with the present invention. The average particle size remains within the above ranges even after the alloy is remelted or recast, although some minor agglomeration does occur.

Another advantage of this process is the remelt capability of the copper-lead alloy without substantial segregation. This effect is desirable particularly if the material is produced as a solid billet which is to be subsequently cast into a desired form. The remelt capability without undesirable segregation may be due to remnants of the homogeneity promoter remaining in the alloy, or may be a function of the fineness of the original dispersion.

Although the homogeneity promoter has a lingering effect in improving the homogeneity of the alloy it may be desirable upon successive remelts, or where the original alloy composition remains molten for an extended period of time, to add the homogeneity promoter in increments. For example, when the alloy remains molten for a period of IO minutes to an hour, a second addition of the promoter in an amount within the preferred effective range should be made prior to using (i.e., casting) the alloy.

Additional additives may be used in combination with the above-described homogeneity promoter. For example, from I to 10 grams of a metal phosphate may be used, such as ortho lead phosphate, ortho cupric phosphate or ortho tin phosphate.

In one method of making the alloy of the present invention, copper of the desired quantity is placed in a graphite crucible and brought to a temperature of l250-l350C using an induction heater. When the copper is melted and has attained the appropriate temperature, as for example about 1275C, the lead and the homogeneity promoter are .added to the melt preferably with stirring. Thereupon violent agitation of the liquid mixture ensues with the formation of gas. The temperature of the mixture is maintained for at least 1 minute and preferably 3 minutes for best results. The melt is then allowed to cool through its solidification temperature during which time the agitation continues. After solidification, the temperature of the alloy is permitted to drop to ambient levels preferably not too slowly. Surprisingly, in spite of the gas evolved during the solidification of the melt, the resulting solid structure of the ingot is free of porosity. After the mixture has been formed it may be cast at conventional temperatures such as l00O-l C.

The novel alloys of copper-lead prepared by the foregoing method have the structural characteristics required to produce optimum anti-frictional qualities. The purity ishigh since the alloy has been thoroughly deoxidized. Also the homogeneity promoter is almost undetectable by emission spectroscopy analysis. The lead phase is finely and randomly dispersed throughout the copper matrix. These factors contribute to a low coefficient of friction in the lifetime of the bearing alloy. They also have a high thermal conductivity and low electrical resistivity. In addition, they may be sintered, fabricated and machined without'losing their superior anti-friction qualities.

The alloy of the present invention is particularlyuseful as a bearing surface. It is suited for use when high or low temperatures and high stresses are present. Most standard methods for making bearings and bearing surfaces may be employed. The bearing can be made by casting techniques, as set forth in greater detail below. Additionally, powder metallurgical techniques are useful. As an example, in bonding the alloy of the present invention to steel, the alloy can be powdered utilizing an atomization method. The steel-is heated, until it turns blue (approximately 600F) and the powder made from the alloy is then sprayed onto the steel surface. The heat from the surface of thesteel bonds the copper-lead alloy to the steel on contact. The powdered alloy can also be sintered onto a steel backing to provide a thicker bearing surface. The bond is strong enough to resist high stresses that result from bearing forces while providing excellent bearing properties.

Another manner in which the alloy of the present invention can be used is as an additive to lubricants. The alloy is combined in powdered form with other lubricants such as greases and oils in quantities ranging preferably from a trace to 4 ounces per pound of the grease or oil. The resulting combination is a lubricant which fully coats moving parts thereby increasing the life of these parts. Maintenance requirements are also reduced. The alloy is of value when the lubricant combination is usedin sealed units where frequent changes of lubricant are uneconomical. In this application, the improved results are obtained over a longer period of time when higher percentages of lead are used in thealloy. The alloysof the present invention may also be of I value in ordnance developments, such-as for small arms ammunition, rotating bands for larger caliber shells, or on the inside surface of gun barrels.

This invention will be illustrated in greater detail by reference to the following embodiments.

EXAMPLES l 6 In these examples, the alloys contained copper to lead in weight proportion of 60 to 40; the total weight of each ingot was one-fourth of a pound. The copper was heated to about l275-in a crucible .in an induction oven. At this temperature, the balance of the lead was added to the copper together with the components shown in the table below. The proportion of components added are listed in gramsfor each pound'of the total of copper and lead. Results are tabulated as per cent segregation in the alloy metals.

TABLE Example Na,CO= Graphite Powder PErcent Segregation l (Control) 100 2 22.5 5-10 3 22.5 6.8 4 4.5 4.5 0 5 12.5 6 2.3 4.5

Examples 3 and 4 resulted in alloys of suitable quality for'bearing materials.

EXAMPLE 7 A powdered mixture was prepared from 2.2 lbs. :of graphite and 4.8 lbs. of sodium carbonate. The mixture was added to a molten alloy comprisingapproximately 20 percent lead, 4 percent'zinc, 75 .percent'copper and minor amounts of antimony, nickel and other constituents. The bath contained about 400 pounds of metal at about 2300-2400F. The molten metal was then centrifugally cast by conventional procedures to form a motor support bearing. The casting proceeded smoothly and the molten metal flowed very well under the centrifugal pressure. Upon cooling, the bearing was broken in a press and the internal structure visually examined. It was observed that excellent dispersion of the constituents of the alloy wasobtained.

EXAMPLE 8 68.4 grams of copper were melted in a graphite crucible at l300C with a Lepel Induction Unit. 456 grams of lead were then added. A mix of 2% Na,co, (2.28 gm) and 0.5 percent powdered graphite (0.57 gm) was added and the mixture was held at l300C for 2 minutes then poured into another cold graphite crucible. The resultant alloy was cooled and examined for segregation. The lead was found to be well dispersed throughout the alloy.

EXAMPLE 9 68.4 grams of copper were melted in a graphite crucible at l300C with a Lepel Induction Unit. 45.6 grams of lead were then added. A mix of 2% CaCO (2.28 gin) and 0.5 percent powdered graphite (0.57 gm) was added and the mixture was held at 1'300C for 2 minutes then poured into another cold graphite crucible. An excellent product was obtained without any serious segregation of the components.

EXAMPLE 10 Nine pounds of copper were placed in an induction heaterand brought to l.300C. Six pounds of lead anda mixture of 68.1 grams of sodium carbonate and 34.1 grams powdered graphite were added to the molten copper. The melt was held at l294C for 2 minutes while being stirred with a graphite rod. The melt was then poured into a split graphite mold, 3 inches in diameter. The casting was allowed to cool for one hour and then removed. The casting showed no lead sweat on its outside surface. It was split and a physical examination showed no lead segregation. A photomicrographic examination of the structure showed a fine dispersion of'the constituents.

The photomicrographs are FIG. 1,, having a magnification -of 50X, and FIG. 2, having a magnification of 250X.'The ,photomicrographs were taken from the bottom of :the ingot where separation and segregation are normally 'con sideredgreater than at the upper portion.

A lineal analysis was made of the particle size and spacing of the sample depicted in the photomicro- Traverses Perpendicular to Axis of Ingot Average Average Standard Distance Standard Particle Deviation Between Deviation Traverse Size Particles No. l 0.0043 mm 0.0020 mm 0.0086 mm 0.0096 mm No. 2 0.0043 mm 0.002l mm 0.0086 mm 0.0082 mm No. 3 0.0043mm 0.0030 mm 0.0086 mm 0.0080 mm Traverses Parallel To Axis of lngot No. l 0.0039 mm '0.00l8'mm 0.0069 mm 0.0047 mm No.2 0.0037mm 0.0015 mm 0.0069 mm 0.0045 mm EXAMPLE 1 l The same procedure set forth in Example 10 was repeated except that the additive comprised 136 grams of calcium carbonate and 34 grams of powdered graphite. An excellent ingot was. obtained which showed no segregation from macroscopic and microscopic exam'inations.

EXAMPLE 12 The same procedure set forth in Example 10 was repeated except that the promoter comprised 136 grams of lithium carbonate and 34 grams of powdered graphite. The melt was poured into the graphite mold which was surrounded with sand, which provided for a slower cooling of the casting. The casting provided an acceptable bearing material; however, it showed a minor amount of segregation.

EXAMPLE 13 The same procedure set forth in Example 10 was repeated except that 12 lbs. of molten copper was prepared and to this 3 lbs. of lead, 0.15 lbs. of tin, 136 grams of sodium carbonate, and 34 grams of powdered graphite were added. The resultant casting was examined macroscopically and microscopically and showed no segregation.

EXAMPLES 14-16 Three castings were made each weighing 15 lbs. The additive used was 136 grams sodium carbonate and 34 grams of graphite in each example. The ratios of copper to lead were 60:40, 70:30, and 80:20, respectively. Each finished casting was then separately melted and poured into a high velocity stream of nitrogen to obtain a fine powder. The powders were sintered and compacted into bearing rings according to conventional techniques. The bearings were examined by the photomicrographic technique and showed a fine dispersion of the constituents. This evidences the excellent remelt capability of the alloys of the present invention and the capability of forming powders for a wide variety of industrial uses. The powder need not be made from a melt of the casting but may be formed directly from a mix of the molten metal and promoter.

The term segregation as used in this application is intended to refer to lead particles having a diameter greater than about lmm. Thealloys of this invention have only a minor amount of segregation, preferably about zero per cent. The massive segregation which occurs without the homogeneity promoter of this invention is normally exhibited as a layering of the lead. Minor segregation is evidenced by lead particles having a size of about 0.5mm, but this is not a serious problem if such particles are well dispersed and constitute less than 5 percent of the lead volume.

This invention has been described in terms of specific embodiments set forth in detail. Alternative embodiments will be apparent to those skilled in the art in view of this disclosure, and accordingly such modifications are to be contemplated within the spirit of the invention as disclosed and claimed herein.

What is claimed is:

l. The method of making a homogeneous copperlead alloy comprising the step of adding an effective amount of a homogeneity promoter to a mixture of molten lead and copper, said promoter comprising elemental carbon and an alkali or alkaline earth metal compound capable of reacting to form a gas.

2. A method according to claim 1 wherein the temperature of said molten lead and copper is maintained in the range of between about l250-1350C for at least 1 minute subsequent to said adding step and thereafter including the step of cooling said molten alloy.

3. A method according to claim 1 wherein the proportions of said promoter are from 1-10 grams carbon and 3-30 grams metal compound per pound of alloy.

4. A method according to claim 1 wherein said promoter is finely powdered graphite and sodium carbonate.

5. A method according to claim 4 wherein the proportion of said gra hite is at least 1 gram, and said sodium carbonate IS a least 3 grams, for each pound of alloy.

6. A method according to claim 1 wherein said promoter is finely powdered graphite and calcium carbonate.

7. A method according to claim 6 wherein the proportion of said graphite is at least 1 gram, and said calcium carbonate is at least 3 grams, for each pound of alloy.

8. A method according to claim 1 wherein said metal compound is a carbonate of a metal selected from Groups la and 2a of the periodic table.

9. A method according to claim 1 wherein said alloy comprises from about 20 to 45 percent lead.

10. A method according to claim 1 wherein said alloy contains up to 10 percent of a metal selected from the group consisting of tin, zinc and combinations thereof.

11. The method of claim 1 wherein said mixture of molten lead and copper is poured into a moving stream of gas to form a finely divided powder.

12. A homogeneous alloy comprising copper and lead, and the product of sodium carbonate and elemental carbon in molten copper and lead.

A 13. A homogeneous alloy comprising copper and lead, and trace remnants from a homogeneity promoter comprising elemental carbon and an alkali or alkaline earth metal compound capable of reacting to form a gas.

14. The alloy of claim 13 comprising about 5 to 55 percent lead, and about to 45 percent copper wherein the lead is in the form of a fine dispersion in a copper matrix, and the average diameter of said lead particles is between about 0.002mm to 0.02mm.

15. The alloy of claim 13 comprising about 20.to 45 percent lead, wherein the lead is in the form of a fine dispersion in a copper matrix, and the average diameter of said lead particles is between about 0.002mm to 0.0lrnm. 

1. The method of making a homogeneous copper-lead alloy comprising the step of adding an effective amount of a homogeneity promoter to a mixture of molten lead and copper, said promoter comprising elemental carbon and an alkali or alkaline earth metal compound capable of reacting to form a gas.
 2. A method according to claim 1 wherein the temperature of said molten lead and copper is maintained in the range of between about 1250*-1350*C for at least 1 minute subsequent to said adding step and thereafter including the step of cooling said molten alloy.
 3. A method according to claim 1 wherein the proportions of said promoter are from 1-10 grams carbon and 3-30 grams metal compound per pound of alloy.
 4. A method according to claim 1 wherein said promoter is finely powdered graphite and sodium carbonate.
 5. A method according to claim 4 wherein the proportion of said graphite is at least 1 gram, and said sodium carbonate is at least 3 grams, for each pound of alloy.
 6. A method according to claim 1 wherein said promoter is finely powdered graphite and calcium carbonate.
 7. A method according to claim 6 wherein the proportion of said graphite is at least 1 gram, and said calcium carbonate is at least 3 grams, for each pound of alloy.
 8. A method according to claim 1 wherein said metal compound is a carbonate of a metal selected from Groups 1a and 2a of the periodic table.
 9. A method according to claim 1 wherein said alloy comprises from about 20 to 45 percent lead.
 10. A method according to claim 1 wherein said alloy contains up to 10 percent of a metal selected from the group consisting of tin, zinc and combinations thereof.
 11. The method of claim 1 wherein said mixture of molten lead and copper is poured into a moving stream of gas to form a finely divided powder.
 12. A homogeneous alloy comprising copper and lead, and the product of sodium carbonate and elemental carbon in molten copper and lead.
 13. A homogeneous alloy comprising copper and lead, and trace remnants from a homogeneity promoter comprising elemental carbon and an alkali or alkaline earth metal compound capable of reacting to form a gas.
 14. The alloy of claim 13 comprising about 5 to 55 percent lead, and about 95 to 45 percent copper wherein the lead is in the form of a fine dispersion in a copper matrix, and the average diameter of said lead particles is between about 0.002mm to 0.02mm. 